Strontium Sr

Discovery

Around 1790 the Edinburgh physicians Adair Crawford and William Cruickshank noticed that a mineral from lead mines near the Scottish village of Strontian differed from known barium minerals. The mineral became known as strontianite.

Thomas Charles Hope and others then showed that it contained a new "earth" (oxide), which could be distinguished from lime and baryta partly by the crimson colour it gave to flames.

Humphry Davy isolated metallic strontium in 1808 by electrolysis. In the same year he used the same technique to isolate barium, calcium and magnesium, opening up the chemistry of the alkaline earth metals.

Origin of the name

The element is named after Strontian, the village in the Scottish Highlands where its ore was first found. The symbol is Sr.

Main uses

• Fireworks and flares: strontium nitrate and carbonate give a deep red flame used in pyrotechnics and distress flares.
• Magnets: strontium ferrite forms cheap, corrosion-resistant permanent magnets found in fridge magnets, small motors and loudspeakers.
• Glow-in-the-dark pigments: europium-doped strontium aluminate stores light and releases it for hours in safety signs and watch dials.
• Cathode-ray tubes: strontium was once added to colour television glass to block X-rays, then its largest use.
• Timekeeping: strontium optical lattice clocks are so precise they would lose less than a second over billions of years.

Isotopes

Natural strontium consists of four stable isotopes, strontium-84, -86, -87 and -88, with strontium-88 making up about 83%. Some strontium-87 is produced by the decay of rubidium-87, so the ratio of strontium-87 to strontium-86 varies from place to place. Archaeologists analyse this ratio in ancient teeth to infer where people grew up. Strontium-90, a fission product with a half-life of about 29 years, is a health concern, while strontium-89 (half-life about 50 days) is used to relieve pain from cancer that has spread to bone.

In everyday life

The main ore of strontium is celestine (strontium sulfate). Traces occur in seawater and food, and once absorbed, strontium follows calcium into bones and teeth. Stable strontium has low toxicity, and strontium salts appear in some toothpastes for sensitive teeth.

Radioactive strontium-90 is a different story. After atmospheric nuclear tests in the 1950s and 1960s, it was detected in children's baby teeth, and these findings helped build public support for the 1963 Partial Test Ban Treaty.